1. Field of the Invention
The present invention relates to a porous metallic material, a porous structural material and a porous decorative sound absorbing material and methods for manufacturing the same, which materials are employed as a sound absorbing member, a catalyst and a building member and excellent in workability, cost, corrosion resistance and decorativeness in appearance, in addition to an excellent sound-absorbing properties thereof.
2. Description of the Prior Art
Hitherto, a porous metallic material is generally produced by a sintering process of a metallic powder or a foaming process of a molten metal. However, the thus produced conventional porous material is a molded product having been molded in a container such as a mold and the like, so that it is poor in workability during bending and the like.
Further, in case that the metallic powder is sintered to form a porous product, a troublesome consideration is required as to an ambient atmospheric condition of a sintering process for the porous product, because it is necessary to mix a low-melting material with the metallic powder before sintering in order to give the thus sintered product a porosity.
On the other hand, hitherto, various types of sound absorbing materials have been employed, which materials are generally classified into three types, that is, a fibrous material such as a glass-wool and the like; a sintered material such as a sintered metal or ceramic; and a concrete material.
It is necessary that the sound absorbing material is excellent in any of sound-absorbing efficiency, sound penetration loss, air-permeability, fire resistance and structural strength. The fibrous material such as the glass-wool and the like is poor in formability and is apt to extremely deteriorate in its sound absorbing efficiency when subjected to a rainy conditon. On the other hand, the sintered material such as the ceramic and the like is poor in impact strength while suffering from its large weight.
Consequently, there is a strong need for a porous metallic material which is excellent in sound absorbing properties and light in weight while provided with a sufficient mechanical strength.
However, in case that the porous metallic material is employed as a sound absorbing material, there are involved the following problems:
Since a porous metallic material having a thickness of from 1 to 2 mm does not serve as a sound absorbing material when it is brought into a rigidly close contact with a rigid body such as a sound-pressure source of an office automation instrument and like instruments, it is necessary to provide a certain air gap between such thin porous metallic material and the rigid body. In order to provide such air gap, channel members or stud members for supporting the porous metallic material are required. In this case, the more the spacing of such members increases, the more the impact absorbing capacity of a structure constructed of the porous metallic material and such members increases. On the other hand, a decrease of the spacing of such members causes the production cost of the structure to be increased, and worsens the structure at its portions adjacent to such channel members or stud members in its impact-absorbing capacity, air-permeability and sound absorbing efficiency.
In addition, in recent years, the field of application of the sound absorbing material has expanded. As a result, the sound absorbing material is widely employed in fields of building materials, office automation instruments and the like, in such fields a decorativeness in appearance is now required of the sound absorbing material.
In order to satisfy the above requirement, a color painting is applied to some conventional porous metallic material. However, such painting gives a surface of the porous metallic material a mottled appearance in color, because pores are not uniformly dispersed in the porous metallic material to lead to different pickup of a painting liquid in the pores under their capillary actions.
Further, the porous metallic material deteriorates its air-permeability when a surface thereof is covered with a plate made of a resin and the like.
On the other hand, there is another conventional material provided with a decoration, which material is constructed of a carpet member or a metallic member for an automobile use, in which member an organic fiber is planted according to a recently advanced fiber planting technique. In case that such fiber planting technique of the organic fiber is applied to a fiber planting treatment of a surface of the porous metallic material, there is a fear that the pores of the porous metallic material are closed with an adhesive applied in its application process which is employed as a pretreatment of the fiber planting treatment.
As described above, in the present state, there is substantially not provided a porous metallic material which is provided with a decorativeness without deteriorating its sound absorbing properties.